Java RMI Programming

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Questions and Answers

What is the purpose of the Naming.lookup() method in RMI?

To generate a stub file and a skeleton file
To compile the implementation class
To invoke the remote object's method
To obtain a reference to the remote object (correct)

What allows a Java programmer to invoke methods on remote objects in a distributed environment?

Remote Method Invocation (RMI) (correct)
Stream programming
Socket programming
Multithreading

What is the purpose of the rmic compiler in Java SE 5 and earlier?

To compile the interface file
To generate a stub file and a skeleton file (correct)
To compile the server class file
To compile the client class file

What is the package used for developing RMI applications in Java?

java.rmi (B) Signup and view all the answers

What is marshalling in RMI?

Converting an object into a byte stream (B) Signup and view all the answers

What is the purpose of registering an interface with a naming service in RMI?

To make the interface publicly available (B) Signup and view all the answers

What happens behind the scenes when a Java programmer invokes a method on a remote object using RMI?

The RMI infrastructure uses byte streams to transfer data and method invocations (A) Signup and view all the answers

What is the primary component of Java that allows for remote method invocation?

java.rmi packages (B) Signup and view all the answers

What is the first step in compiling and executing an RMI application?

Compile all files with javac (C) Signup and view all the answers

What is the purpose of a stub in RMI?

To act as a proxy for the remote object on the client side (C) Signup and view all the answers

What happens when the RMI Registry is started?

The command window’s title changes (A) Signup and view all the answers

What is the purpose of the RMI registry?

To register remote objects with the naming service (A) Signup and view all the answers

What is unmarshalling in RMI?

Converting a byte stream into an object (A) Signup and view all the answers

What is the purpose of marshalling and unmarshalling in RMI?

To convert Java objects into byte streams and vice versa (C) Signup and view all the answers

What is the term for the process of converting a byte stream back into an object in RMI?

Unmarshalling (B) Signup and view all the answers

What is the role of the stub in RMI?

To act as a proxy for the remote object on the client side (D) Signup and view all the answers

What is the command to start the RMI Registry?

rmiregistry (C) Signup and view all the answers

What is marshalling in the context of RMI?

Converting an object into a byte stream (B) Signup and view all the answers

What is the purpose of the RMI Registry?

To register the remote objects (B) Signup and view all the answers

What is the correct order of steps to implement RMI?

Start the RMI Registry, run the server, run the client (C) Signup and view all the answers

What is the strategy used in this example for RMI implementation?

Using a single instance of the implementation class to hold instance(s) of a class (D) Signup and view all the answers

What is the purpose of the skeleton in RMI?

To act as a proxy for the remote object on the server side (B) Signup and view all the answers

What is the package used in Java for RMI?

java.rmi (D) Signup and view all the answers

What needs to be closed down after the client process has finished?

The server process and the RMI Registry (D) Signup and view all the answers

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Study Notes

Remote Method Invocation (RMI)

RMI provides a platform-independent means of invoking methods on remote objects (i.e., objects located on other systems).
Under RMI, the networking details required by explicit programming of streams and sockets disappear, and the fact that an object is located remotely is almost transparent to the Java programmer.

RMI Process

The server program registers an interface with a naming service, making it accessible by client programs.
The interface contains the signatures for those methods of the object that the server wishes to make publicly available.

Compilation and Execution

Compile all files with javac:
- javac Hello.java
- javac HelloImpl.java
- javac HelloServer.java
- javac HelloClient.java
Before Java SE 5, it was necessary to compile the implementation class with the rmic compiler to generate a stub file and a skeleton file.

Running the RMI Application

Step 1: Compile all files with javac.
Step 2: Start the RMI Registry using rmiregistry.
Step 3: Run the Server using java HelloServer in a new window.
Step 4: Run the Client using java HelloClient in a third window.

Using RMI Meaningfully

In a realistic RMI application, multiple methods and probably multiple objects will be employed.
Two possible strategies for implementing RMI applications:
- Use a single instance of the implementation class to hold instance(s) of a class whose methods are to be called remotely.
- Use the implementation class directly for storing required data and methods, creating instances of this class.